1. Field of the Invention
The present invention relates to an image display apparatus.
2. Description of the Related Art
Conventionally, there has been known an image display apparatus using an electron emitting apparatus which utilizes an electron emitting device. As an example of the image display apparatus, there is a flat electron beam display panel having an electron source substrate (rear plate) and an anode substrate (faceplate). The rear plate has a plurality of cold-cathode electron emitting devices. The face plate has a plurality of phosphors respectively facing a plurality of electron emitting devices and an anode electrode (a metal back or a transparent electrode) covering the phosphors. When a voltage is applied to between the electron emitting device and the anode electrode, electrons emitted from the electron emitting device are accelerated and collide with the phosphor, whereby the phosphor emits light, and an image is displayed.
The electron emitting device has a cathode electrode, a gate electrode, and an electron emitting portion. The cathode electrode is connected to a cathode wiring (a scanning wiring), and the gate electrode is connected to a gate wiring (a signal wiring) and having a resistance higher than the resistance of the scanning wiring. A voltage is applied to between the cathode electrode and the gate electrode through each of those wirings, whereby electrons are emitted from the electron emitting portions.
In this image display apparatus, it is desirable that the electron emitting devices have uniform electron emission characteristics (the amount of emitted electrons to a voltage; emission current Ie). However, it is difficult to produce a plurality of electron emitting devices so that the electron emission characteristics are uniformized. Therefore, in the related art, a resistive element (a ballast resistance) with a large resistance value is connected to between the cathode electrode and the scanning wiring, and consequently, variation in the electron emission characteristics is reduced.
Further, in the above image display apparatus, in order to obtain a high emission luminance, a high voltage is applied to between the electron emitting device and the anode electrode. The electrons emitted from the electron emitting device are scattered until reaching the phosphor and the anode electrode. Thus, in order to realize a high-definition image display apparatus (a display), the distance between the electron emitting device and the anode electrode is reduced.
Therefore, a high electric field is formed between the face plate and the rear plate, and accidental electrical discharge may occur therebetween, resulting in, for example, breaking of the electron emitting device and a failure of a drive circuit for use in the application of a voltage to the cathode electrode and the gate electrode. Specifically, an accidental large current (a discharge current) due to electrical discharge is applied into the drive circuit, leading to a failure of the drive circuit. A failure of a drive circuit, connected to a signal wiring with a small power capacity, easily occurs compared to a drive circuit connected to a scanning wiring. When an accidental large current (a discharge current) due to electrical discharge is applied into the electron emitting device, not only the electron emitting device is broken, but also a potential on the gate electrode is increased due to wiring resistance. Consequently, a high potential is applied to adjacent devices connected through the signal wiring, leading to an effect on a discharge current of the adjacent devices.
Thus, only by connecting the ballast resistance to between the cathode electrode and the scanning wiring, there cannot be solved a problem that the electron emission amount is varied due to accidental electrical discharge.
In order to solve the above problem that occurs when a discharge occurs, the impedance of the scanning wiring may be rendered lower than the impedance of the signal wiring. Namely, a discharge current may be applied to the drive circuit connected to the scanning wiring. Specifically, a resistive element A may be connected to between the signal wiring and the gate electrode. This configuration is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-157757.
Japanese Patent Application Laid-Open No. 2003-157757 discloses suppression of the inflow of a discharge current into the signal wiring, but does not disclose reduction of the variation in the electron emission characteristics. Although Japanese Patent Application Laid-Open No. 2003-157757 discloses that a resistive element B is connected to between the scanning wiring and the cathode electrode, a discharge current is not applied to the signal wiring, and therefore, the resistance value of the resistive element B is set to be smaller than the resistance value of the resistive element A. Therefore, the resistive element B does not function as a ballast resistance sufficiently, and thus, the variation in the electron emission characteristics cannot be reduced upon normal driving.
Meanwhile, when the resistance value of the resistive element B is rendered larger to such an extent that the resistive element B expresses the function as a ballast resistance, while maintaining such a relation that the resistance value of the resistive element A is larger than the resistance value of the resistive element B, the resistance value of the resistive element A is also increased with the increase of the resistance value of the resistive element B. Therefore, there arises a problem that the electron emitting device cannot be driven.